A fading radius valley towards M-dwarfs, a persistent density valley across stellar types

Abstract

The radius valley separating super-Earths from mini-Neptunes is a fundamental benchmark for theories of planet formation and evolution. Observations show that the location of the radius valley decreases with decreasing stellar mass and with increasing orbital period. Here, we build from our previous pebble-based formation model, which, combined with photoevaporation after disc dispersal, unveiled the radius valley as a separator between rocky- and water-worlds. We expand our models for a range of stellar masses spanning from 0.1 to 1.5 $M_{\odot }$. We find that the location of the radius valley is well described by a power-law in stellar mass as $R_{\mathrm{valley}}=1.8197M_{\star }^{0.14(+0.02/-0.01)}$, which is in excellent agreement with observations. We also find very good agreement with the dependence of the radius valley on orbital period, both for FGK- and M-dwarfs. Additionally, we note that the radius valley gets filled towards low stellar masses, particularly at 0.1-0.4 $M_{\odot }$, yielding a rather flat slope in $R_{\mathrm{valley}}-P_{\mathrm{orb}}$. This is the result of orbital migration occurring at lower planet mass for less massive stars, which allows for low-mass water-worlds to reach the inner regions of the system, blurring the separation in mass (and size) between rocky- and water-worlds. Furthermore, we find that for planetary equilibrium temperatures above 400 K, the water in the volatile layer exists fully in the form of steam, puffing the planet radius up compared to condensed-water worlds. This produces an increase in planet radii of $\sim 30\%$ at 1 $M_{\oplus }$, and of $\sim 15\%$ at 5 $M_{\oplus }$, compared to condensed-water-worlds. As with Sun-like stars, pebble accretion leaves its imprint on the overall exoplanet population as a depletion of planets with intermediate compositions, carving a valley in planet density for all spectral types (abridged).

arXiv commentAccepted for publication in A&A Letters. Results from simulations available at https://zenodo.org/records/10719523

References in corpus (84)

• The Transiting Exoplanet Survey Satellite
• New evolutionary models for pre-main sequence and main sequence low-mass stars down to the hydrogen-burning limit
• The California-Kepler Survey. III. A Gap in the Radius Distribution of Small Planets
• Using FU Orionis Outbursts to Constrain Self-Regulated Protostellar Disk Models
• Mass-Radius Relationships for Solid Exoplanets
• The evaporation valley in the Kepler planets
• Growth Model Interpretation of Planet Size Distribution
• On the radiative equilibrium of irradiated planetary atmospheres
• A torque formula for non-isothermal Type I planetary migration - II. Effects of diffusion
• The California Kepler Survey VII. Precise Planet Radii Leveraging Gaia DR2 Reveal the Stellar Mass Dependence of the Planet Radius Gap
• An asteroseismic view of the radius valley: stripped cores, not born rocky
• The Role of Core Mass in Controlling Evaporation: the Kepler Radius Distribution and the Kepler-36 Density Dichotomy
• Core-powered mass loss and the radius distribution of small exoplanets
• Separating gas-giant and ice-giant planets by halting pebble accretion
• Planetary evaporation by UV & X-ray radiation: basic hydrodynamics
• Protoplanetary Disk Structures in Ophiuchus II: Extension to Fainter Sources
• Sculpting the Valley in the Radius Distribution of Small Exoplanets as a by-product of Planet Formation: The Core-Powered Mass-Loss Mechanism
• Breaking the Chains: Hot Super-Earth systems from migration and disruption of compact resonant chains
• Gaseous Mean Opacities for Giant Planet and Ultracool Dwarf Atmospheres over a Range of Metallicities and Temperatures
• The stickiness of micrometer-sized water-ice particles
• Pebble isolation mass --- scaling law and implications for the formation of super-Earths and gas giants
• Density, not radius, separates rocky and water-rich small planets orbiting M dwarf stars
• The CHEOPS mission
• Planetesimal formation starts at the snow line
• Compositional imprints in density-distance-time: a rocky composition for close-in low-mass exoplanets from the location of the valley of evaporation
• Dust size distributions in coagulation/fragmentation equilibrium: Numerical solutions and analytical fits
• The Exoplanet Population Observation Simulator. I - The Inner Edges of Planetary Systems
• Evolutionary Analysis of Gaseous Sub-Neptune-Mass Planets with MESA
• Close-in planetesimal formation by pile-up of drifting pebbles
• The New Generation Planetary Population Synthesis (NGPPS). IV. Planetary systems around low-mass stars
• Hydrodynamics of Embedded Planets' First Atmospheres. II. A Rapid Recycling of Atmospheric Gas
• Theoretical models of planetary system formation: mass vs semi-major axis
• Contacts of Water Ice in Protoplanetary Disks - Laboratory Experiments
• The Gaia-Kepler Stellar Properties Catalog. II. Planet Radius Demographics as a Function of Stellar Mass and Age
• A new equation of state for dense hydrogen-helium mixtures
• How drifting and evaporating pebbles shape giant planets I: Heavy element content and atmospheric C/O
• The Formation of Super-Earths and Mini-Neptunes with Giant Impacts
• Evolution of the radius valley around low mass stars from $Kepler$ and $K2$
• A non-grey analytical model for irradiated atmospheres. I: Derivation
• AQUA: A Collection of H${}_2$O Equations of State for Planetary Models
• The California-Kepler Survey. X. The Radius Gap as a Function of Stellar Mass, Metallicity, and Age
• Metallicity, planet formation, and disc lifetimes
• Searching the Entirety of Kepler Data. II. Occurrence Rate Estimates for FGK Stars
• Planetary evolution with atmospheric photoevaporation I. Analytical derivation and numerical study of the evaporation valley and transition from super-Earths to sub-Neptunes
• Mass-radius relationships for irradiated ocean planets
• A Spectroscopic Analysis of the California-Kepler Survey Sample: I. Stellar Parameters, Planetary Radii and a Slope in the Radius Gap
• Photoevaporation vs. core-powered mass-loss: model comparison with the 3D radius gap
• The formation of Jupiter by hybrid pebble-planetesimal accretion
• Empirical constraints on turbulence in proto-planetary discs
• A non-grey analytical model for irradiated atmospheres. II: Analytical vs. numerical solutions
• Migration-driven diversity of super-Earth compositions
• A super-Earth and a sub-Neptune orbiting the bright, quiet M3 dwarf TOI-1266
• Planetesimal Population Synthesis: Pebble Flux Regulated Planetesimal Formation
• Primordial Radius Gap and Potentially Broad Core Mass Distributions of Super-Earths and Sub-Neptunes
• The runaway greenhouse radius inflation effect - An observational diagnostic to probe water on Earth-size planets and test the Habitable Zone concept
• A Systematic Study of the Final Masses of Gas Giant Planets
• Planet formation and migration near the silicate sublimation front in protoplanetary disks
• Ice Grain Collisions in Comparison: CO${}_2$, H${}_2$O and their Mixtures
• How dust fragmentation may be beneficial to planetary growth by pebble accretion
• The sub-Neptune desert and its dependence on stellar type: Controlled by lifetime X-ray irradiation
• A deep radius valley revealed by Kepler short cadence observations
• Migrating super-Earths in low-viscosity discs: unveiling the roles of feedback, vortices, and laminar accretion flows
• Giant planet formation at the pressure maxima of protoplanetary disks II. A hybrid accretion scenario
• Most super-Earths formed by dry pebble accretion are less massive than 5 Earth masses
• Current Population Statistics Do Not Favor Photoevaporation over Core-Powered Mass Loss as the Dominant Cause of the Exoplanet Radius Gap
• Pebbles versus planetesimals: the outcomes of population synthesis models
• Formation of solar system analogs I: looking for initial conditions through a population synthesis analysis
• The maximum mass of planetary embryos formed in core-accretion models
• Thermal torque effects on the migration of growing low-mass planets
• A cool runaway greenhouse without surface magma ocean
• Atmospheric Erosion by Giant Impacts onto Terrestrial Planets
• How to make giant planets via pebble accretion
• Giant planet formation at the pressure maxima of protoplanetary disks
• Recycling of the first atmospheres of embedded planets: Dependence on core mass and optical depth
• Atmospheric Recyling of Volatiles by Pebble-Accreting Planets
• Unified simulations of planetary formation and atmospheric evolution: Effects of pebble accretion, giant impacts, and stellar irradiations on super-Earth formation
• Three new brown dwarfs and a massive hot Jupiter revealed by TESS around early-type stars
• Using Deep Neural Networks to compute the mass of forming planets
• Unified simulations of planetary formation and atmospheric evolution II: Rapid disk clearing by photoevaporation yields low-mass super-Earth atmospheres
• The interplay between pebble and planetesimal accretion in population synthesis models and its role in giant planet formation
• Growth of Aggregates with Liquid-Like Ice-Shells in Protoplanetary Discs
• The formation of giant planets in wide orbits by photoevaporation-synchronised migration
• Size evolution of close-in super-Earths through giant impacts and photoevaporation
• Planetary mass-radius relations across the galaxy

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• From super-Earths to sub-Neptunes: Observational constraints and connections to theoretical models
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• Three super-Earths and a possible water world from TESS and ESPRESSO
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• TESS discovery of two super-Earths orbiting the M-dwarf stars TOI-6002 and TOI-5713 near the radius valley
• Using the helium triplet as a tracer of the physics of giant planet outflows
• Characterisation of TOI-406 as showcase of the THIRSTEE program: A 2-planet system straddling the M-dwarf density gap
• Water-Cooled (sub)-Neptunes Get Better Gas Mileage
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• TESS and HARPS-N unveil two planets transiting TOI-1453. A super-Earth and one of the lowest mass sub-Neptunes
• Super-Earth masses and stellar abundances from NIRPS reveal tentative evidence for water-rich formation around M dwarfs
• The PAIRS project: a global formation model for planets in binaries. I. Effect of disc truncation on the growth of S-type planets
• A transiting rocky super-Earth and a non-transiting sub-Neptune orbiting the M dwarf TOI-771
• On the Ordering of Exoplanet Systems
• Densities of small planets around the M dwarfs TOI-4336 A and TOI-4342 with ESPRESSO: Three sub-Neptunes, one super-Earth, and a Neptune-mass candidate
• A Validated Low-to-Intermediate Mass Planetary Interior Structure Model and New Mass-Radius Relations
• Evolution and Observable Properties of Rocky Planet Atmospheres
• Precise Parameters from Bayesian SED Fitting Indicate Thermally-Driven Mass Loss Likely Driver of Radius Valley
• The GAPS programme at TNG LXXI. A sub-Neptune suitable for atmospheric characterization in a multiplanet and mutually inclined system orbiting the bright K dwarf TOI-5789 (HIP 99452)
• Gas-depleted planet formation occurred in the four-planet system around the red dwarf LHS 1903
• A planet-host ratio relation to synthesize microlensing and transiting exoplanet demography from Roman
• Revisiting the exoplanet radius valley with host stars from SWEET-Cat
• Sibling Sub-Neptunes Around Sibling M Dwarfs: TOI-521 and TOI-912